Based on adsorbent theory and the law of energy change, the degree of interaction on the surface is determined. The adsorbent layer is defined. Analysis calculation formula on the thickness of adsorbent layer is obtained. The thickness of adsorbent layer is the most critical factor for thin film lubrication research, and is a critical point to the difference between thin film and thick film analyzed. According to the theory of interaction of molecules and basic definition of hydromechanics, correcting model of viscosity with exponential function is derived. It can be used to determine the law of change of fluid viscosity in micro-clearance, and thus the rationale is provided for theoretic model of thin film lubrication established.